1. Field of the Invention
This invention relates to an imaging apparatus. This invention particularly relates to an imaging apparatus, which is provided with an electrostatic recording material, which records image information as an electrostatic latent image, and which generates electric currents in accordance with the recorded electrostatic latent image when a read-out surface of the electrostatic recording material is scanned with a reading electromagnetic wave.
2. Description of the Related Art
Methods and apparatuses for recording and reading out radiation image information by utilizing image detectors have heretofore been proposed. With the proposed methods and apparatuses for recording and reading out radiation image information, such that a radiation dose delivered to an object during a medical radiation image recording operation may be kept small, and such that the image quality of an image and its capability of serving as an effective tool in, particularly, the efficient and accurate diagnosis of an illness may be enhanced, an electrostatic recording material, which is provided with a photo-conductive material sensitive to radiation (such as X-rays), e.g. a selenium plate constituted of axe2x80x94Se, or the like, is employed as an image detector. The image detector is exposed to radiation, such as X-rays, carrying radiation image information, and electric charges occurring in an amount proportional to the dose of the radiation delivered to the image detector are accumulated as latent image charges in a charge accumulating section formed within the image detector. In this manner, the radiation image information is recorded as an electrostatic latent image at the charge accumulating section. Thereafter, the image detector, on which the radiation image information has been recorded, is scanned with a laser beam or line light acting as reading light, and the radiation image information is thereby read out from the image detector. The methods and apparatuses for recording and reading out radiation image information by utilizing image detectors are described in, for example, U.S. Pat. No. 5,268,569, PCT International Publication No. WO 98/59261, Japanese Unexamined Patent Publication No. 9(1997)-5906, and Japanese Patent Application Nos. 10(1998)-232824, 11(1999)-242876, and 11(1999)-87922.
The electrostatic recording material described above comprises a plurality of layers, such as electrode layers and photo-conductive material layers. Ordinarily, the plurality of the layers are overlaid successively on a glass substrate. As the glass substrate, a thin glass plate having a thickness of at most 1.1 mm, which is ordinarily employed in a liquid crystal display device, is appropriate. The thin glass plate employed in the liquid crystal display device has good chemical resistance, good heat resistance, and the like, which are necessary for the formation of the electrostatic recording material. Also, the thin glass plate employed in the liquid crystal display device is capable of being produced at a low cost.
In cases where the electrostatic recording material is utilized as the image detector of the radiation image recording and read-out apparatus, which is constituted as, for example, a chest image recording and read-out apparatus, it is necessary for a flat plate-shaped image detector having a size of approximately 40 cmxc3x9740 cm to be located so as to stand facing the chest of an object standing upright.
However, in cases where the electrostatic recording material is located, for example, vertically as described above, since the electrostatic recording material is supported merely by the thin glass substrate, if end regions of the electrostatic recording material are merely held by holding means, the middle region of the electrostatic recording material will bend. As a result, the problems will occur in that the distance between a reading light source and the electrostatic recording material varies for different sites on the electrostatic recording material, and sharpness of an image, which is obtained from an operation for reading out the electrostatic latent image from the electrostatic recording material, becomes partially low. The decrease in the image sharpness presents a very real problem in the chest image recording and read-out apparatus, and the like, which should yield an accurate image appropriate for the use as a medical image. Also, the problems occur in that thin glass substrate has a low strength and breaks when certain impacts are given to the chest image recording and read-out apparatus, and the like.
The primary object of the present invention is to provide an imaging apparatus, wherein sharpness of an image, which is obtained from an operation for reading out an electrostatic latent image from an electrostatic recording material, is kept high, and wherein the apparatus has an enhanced strength.
The present invention provides an imaging apparatus, comprising:
i) a planar electrostatic recording material, which records image information as an electrostatic latent image, and which generates electric currents in accordance with the electrostatic latent image when a read-out surface of the planar electrostatic recording material is scanned with a reading electromagnetic wave,
ii) a flat plate-shaped substrate, which supports the electrostatic recording material from a side of the read-out surface, and which has permeability with respect to the reading electromagnetic wave, and
iii) a flat plate-shaped base plate for supporting the flat plate-shaped substrate from a side opposite to a surface of the substrate, on which surface the electrostatic recording material is formed, the flat plate-shaped base plate having a rigidity higher than the rigidity of the substrate and having permeability with respect to the reading electromagnetic wave.
As the electrostatic recording material, an electrostatic recording material maybe employed, which is capable of recording image information as an electrostatic latent image when being exposed to light (not limited to visible light) carrying the image information. Alternatively, an electrostatic recording material may be employed, which is capable of recording radiation image information as an electrostatic latent image when being exposed to radiation carrying the radiation image information of an object.
In the imaging apparatus in accordance with the present invention, the flat plate-shaped base plate has a rigidity higher than the rigidity of the substrate. Specifically, the base plate may be formed from a material having a rigidity higher than the rigidity of a material constituting the substrate. Alternatively, the base plate and the substrate may be formed from the same material, and the thickness of the base plate may be larger than the thickness of the substrate, such that the base plate may have a rigidity higher than the rigidity of the substrate.
The reading electromagnetic wave may be one of various kinds of electromagnetic waves, with which the electric charges in the electrostatic recording material are capable of being caused to move, and with which the electrostatic latent image is capable of being read out electrically from the electrostatic recording material. Specifically, the reading electromagnetic wave may be light, radiation, or the like. The reading electromagnetic wave passes through the base plate and the substrate and then impinges upon the read-out surface of the electrostatic recording material.
The base plate should preferably have a coefficient of thermal expansion approximately identical with the coefficient of thermal expansion of the substrate.
Also, the base plate should preferably have a refractive index approximately identical with the refractive index of the substrate.
Further, a surface of the base plate and a surface of the substrate, which surfaces stand facing each other, should preferably be adhered by an adhesive agent to each other.
In such cases, the adhesive agent may be selected in accordance with the materials constituting the base plate and the substrate. Specifically, in cases where the base plate and the substrate are constituted of glass, an epoxy resin, Canada balsam, or the like, may be employed as the adhesive agent.
Furthermore, an anti-reflection coating layer for preventing reflection of the reading electromagnetic wave should preferably be formed on a light entry face of the base plate, upon which light entry face the reading electromagnetic wave is incident.
With the imaging apparatus in accordance with the present invention, the substrate for supporting the electrostatic recording material is supported by the base plate, which has the rigidity higher than the rigidity of the substrate. Therefore, in cases where the electrostatic recording material is located in one of various orientations, for example, in a vertical orientation, the middle region of the electrostatic recording material does not bend. Accordingly, an image having high sharpness is capable of being obtained from the operation for reading out the electrostatic latent image. The imaging apparatus in accordance with the present invention is advantageous particularly for obtaining a medical image, which should have a high image sharpness.
Also, with the imaging apparatus in accordance with the present invention, which is provided with the base plate, the resistance to impacts given to the apparatus, and the like, is capable of being kept higher than in an imaging apparatus, in which no base plate is provided and only the substrate is provided.
With the imaging apparatus in accordance with the present invention, wherein the base plate has a coefficient of thermal expansion approximately identical with the coefficient of thermal expansion of the substrate, the base plate and the substrate are capable of being prevented from separating from each other when the temperature changes due to a change in environmental conditions of the apparatus, and the like.
With the imaging apparatus in accordance with the present invention, wherein the base plate has a refractive index approximately identical with the refractive index of the substrate, light loss and stray light are capable of being prevented from occurring due to reflection of the reading electromagnetic wave (reading light) from an interface between the base plate and the substrate. In cases where the reflection of the reading light from the interface between the base plate and the substrate is thus prevented, the sharpness of the read-out image is capable of being enhanced.
With the imaging apparatus in accordance with the present invention, wherein the surface of the base plate and the surface of the substrate, which surfaces stand facing each other, are adhered by the adhesive agent to each other, the base plate and the substrate are capable of being prevented from separating easily from each other.
With the imaging apparatus in accordance with the present invention, wherein the anti-reflection coating layer for preventing reflection of the reading electromagnetic wave is formed on the light entry face of the base plate, upon which light entry face the reading electromagnetic wave is incident, light loss and stray light are capable of being prevented from occurring due to reflection of the reading electromagnetic wave from the light entry face of the base plate. Therefore, the sharpness of the read-out image is capable of being enhanced.